Conventionally, an electric vehicle charges its battery, which is used as a power source for driving the vehicle, at a charge station (i.e., a charge point). Japanese Patent Laid-Open No. 2003-262525 (JP '525) and Japanese Patent Laid-Open No. 2011-252816 (JP '816) disclose a technique to provide information of charge stations around a current position of the vehicle.
Further, Japanese Patent Laid-Open No. 2000-46571 (JP '571) discloses a technique that calculates a travel distance of the vehicle based upon the remaining energy of the battery (i.e., a currently-reserved energy). Based on the travel distance calculated, JP '571 notifies the user (e.g., driver) of the need to charge the battery at a nearest energy supply facility (i.e., nearest charge station) when the travel distance calculated is shorter than a distance to a second nearest energy supply facility.
The technique disclosed in JP '571 determines a reachability of an energy supply facility based on a calculation of a travelable distance according to a remaining energy of the electric vehicle, and a comparison between the travelable distance calculated and a distance to the energy supply facility.
However, when accurately determining reachability of the energy supply facility, it is necessary to search for a route to the energy supply facility in consideration of an ever-changing traffic situation that may be caused by, for example traffic congestion, and to calculate a required energy for traveling the searched route.
Further, for example, multiple candidates of the energy supply facility may be presented by a navigation system to the user of the vehicle. Therefore, the required energy to reach the facilities may have to be respectively calculated in addition to a route search for each of those facilities.
Furthermore, the travel of the vehicle results in a position change of the vehicle, thereby causing continuous change of the route from the vehicle to the energy supply facility and causing calculations and re-calculations of the required energy of such ever-changing route to the facility. If the ever-changing traffic situation, such as the congestion condition, is reflected in the calculations of the required energy, an in-vehicle computer may become over-loaded by such calculations.
Therefore, such calculations may be processed by a center computer having a higher processing capacity. However, even in such a situation, the center computer may also be over-loaded by such calculations if many vehicles request the center computer to provide such calculations with the same calculation level (e.g., quality) as the one performed in each of the vehicles.